Automatically changeable printed signs are now commonly used for destination signs on buses and trains. Destination signs must be changeable according to the particular route of the vehicle and each sign must be capable of displaying a large number of different destination names. The typical destination name requires many different alphanumeric characters and the sign must be changeable quickly from one name to another. A destination sign, which is now in common use, is capable of displaying any desired destination name by forming multiple side-by-side alphanumeric characters with any desired character at a given character location. In such a destination sign, each character is formed by a character module which includes printed roller tapes for displaying any desired character by properly positioning the tapes in the module. The individual tapes of a module carry plural segments of different characters and the tapes of the module must be positioned relative to each other such that all segments of a given character may be displayed together. This sign has the advantage of being able to form any combination of characters with the use of relatively short display tapes. Such a destination sign is disclosed and claimed in U.S. Pat. No. 4,064,502 granted Dec. 20, 1977, to William H. Saylor et al.
In a changeable alphanumeric sign of the type referred to above, the changing of the sign from one destination name to another is entirely automatic. The operator of the vehicle merely selects the desired destination name by setting an input device to a number corresponding to the desired destination name. For example, the operator has at his drivers position a set of number wheels and a look-up table containing a list of destination names and the corresponding number. The desired destination name is selected by setting the number wheels to the number and the sign is automatically changed to display the selected name. The selected destination name is presented by an alphanumeric display of the sign on the front of the bus and, in most cases, at another sign on the side of the bus. These destination signs are not within the view of the vehicle operator.
Because of the large number of destination names on the operators look-up table and because of human error, there is some chance that the wrong destination name will be selected. Such an error may also occur because of malfunction in the automatic sign itself. It is desirable, therefore, to provide means for reducing the likelihood of a wrong name being displayed by the destination sign.
A general objective of this invention is to provide a message monitor in combination with a bus destination sign.